From c265ddb784d08d7acf4c26beb585527cd40534c7 Mon Sep 17 00:00:00 2001 From: "Dirk O. Kaar" Date: Tue, 21 Jan 2020 12:40:32 +0100 Subject: [PATCH 1/2] Greatly reduces error rate (half, or 0 zero errors, depends on in/out ranges) for round-trip mapping at the same performance. (Based on "improved_map" from ESP8266's Servo.cpp) --- cores/arduino/WMath.cpp | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/cores/arduino/WMath.cpp b/cores/arduino/WMath.cpp index 9fb072f46..8d9975e3f 100644 --- a/cores/arduino/WMath.cpp +++ b/cores/arduino/WMath.cpp @@ -49,9 +49,12 @@ long random(long howsmall, long howbig) return random(diff) + howsmall; } -long map(long x, long in_min, long in_max, long out_min, long out_max) -{ - return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min; +long map(long x, long in_min, long in_max, long out_min, long out_max) { + const long dividend = out_max - out_min; + const long divisor = in_max - in_min; + const long delta = x - in_min; + + return (delta * dividend + (divisor / 2)) / divisor + out_min; } unsigned int makeWord(unsigned int w) { return w; } From b02d22a2e2f4498d3e6fbc94df3068ad5031f2e2 Mon Sep 17 00:00:00 2001 From: "Dirk O. Kaar" Date: Sat, 6 Feb 2021 20:27:14 +0100 Subject: [PATCH 2/2] Clarify input constraints via comment. --- cores/arduino/WMath.cpp | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/cores/arduino/WMath.cpp b/cores/arduino/WMath.cpp index 8d9975e3f..247daca69 100644 --- a/cores/arduino/WMath.cpp +++ b/cores/arduino/WMath.cpp @@ -49,7 +49,10 @@ long random(long howsmall, long howbig) return random(diff) + howsmall; } -long map(long x, long in_min, long in_max, long out_min, long out_max) { +// well-defined for in_min < in_max, in_min <= x <= in_max, +// out_min <= out_max +long map(long x, long in_min, long in_max, long out_min, long out_max) +{ const long dividend = out_max - out_min; const long divisor = in_max - in_min; const long delta = x - in_min;